Analog transmission techniques have historically been the dominant method of conveying content to television viewers. The advent of low cost digital signal processing devices has enabled the consumer to receive digital television. Digital conveyance of television signals has become commonplace, and the advantage of digital transmission over analog is evidenced by the continued displacement of analog channels with digital channels. In fact, digital transmission techniques have proven to be a key factor in the rapid growth and diversity of the type of content offered over digital television mediums such as satellite, terrestrial cable, and terrestrial “over-air” television.
The benefit of digital transmission techniques is recognized and valued by content providers and television viewers alike. The compression and signal replication mechanisms inherent in digital transmission offers channel densities and signal quality far superior to conventional analog television.
Digital television transmission has enabled the public to enjoy an enhanced television viewing experience. The digital television viewer can choose from a significantly larger selection of channels than could ever be transmitted using conventional analog techniques. Further, unlike its analog counterpart, digital transmissions deliver consistently high quality presentation of received content to the television viewer due their inherent insensitivity to impairments in the signal path.
Unfortunately, the very process that enables the numerous positive attributes of digital reception carries with it some negative consequences. The process of receiving a digital signal has the distinct disadvantage of introducing a noticeable time delay between the received signal and the presentation of the content to the viewer. The delay does not degrade the experience while watching a program, however, it is noticeable and can be quite annoying to the television viewer as one switches from one channel to another.
Analog television systems, in contrast, introduce virtually no perceivable time delay between the time that the signal is received and the time it is displayed. In fact, unlike digital transmission methods, the typical analog reception process requires no time-dependant processing of the signal and thus presents received content to the user almost instantaneously.
A digital presentation stream comprises digitized content fragmented into a contiguous stream of digitized data. The data needs to be received and reassembled into a logical block, or frame, before it can be properly conveyed to a television viewer. The amount of time needed to initially convey the content to a user is dependant upon the algorithm used to encode the content, and the proximity to the next valid block of received content. The reception process often results in a delay of one-half second or more between the time that a channel is first selected and the time that is presented to the user.
The absence of any perceivable time delay is a desirable attribute exhibited by an analog television receiver. This allows a user to switch between channels and experience almost no detectable delay between the time that a channel is selected and the time that the new channel is presented. The typical television viewer is highly accustomed to the speed that one can view a new channel after being switched from a previous channel. The ability to rapidly view and switch channels has led to common viewing behaviors such as “channel surfing” where the user samples one or more channels, often in rapid succession. Other typical viewing behaviors include switching among channels in a group of favorite channels and switching between channels in a group of recently viewed channels. The behaviors noted here are by no means exhaustive, and serve only to illustrate the point that the ability to rapidly switch and view new channels is a key facet of any modern analog television receiver. The imposition of any technical constraint that, among other things, hinders the ability to rapidly switch and view new channels is likely to be considered objectionable by typical television users.
A possible solution to eliminating the negative effect of time delay experienced in viewing digital television transmissions is to build a receiving unit capable of simultaneously receiving and processing every possible channel available to the user. A user with such a device could switch between the outputs of preprocessed channels within the device. The fact that the channels are preprocessed would eliminate the objectionable time delay that results when initially processing a newly received digital channel.
The cost and complexity of a unit capable of simultaneously receiving and processing every digital channel available to the television user would be exceedingly impractical. Recognizing this, some receivers provide two tuners. While one tuner is used to receive and process one channel, the receiver uses the second tuner to receive a second channel. These conventional receivers attempt to reduce channel switching latency by predicting what channel a user will tune to next. Although predictions can be made using simple prediction rules, such as simple channel surfing behavior where channels are selected in sequential fashion, conventional receivers do a poor job of eliminating delays except in some limited use cases.
There is a significant need for a practical means of substantially eliminating the effect of the time delay associated with receiving and processing digital television transmissions. The substantial elimination of the effect of the time delay would significantly enhance the user experience by allowing one to enjoy the best attributes that digital television offers while retaining the essentially instantaneous channel changing performance that analog receivers exhibit.